This disclosure is directed to a solder control system, and more particularly to a solder control system which enables the operator to make periodic adjustments in the operation of the solder control system. It is especially helpful in controlled repair of a printed circuit board (PCB) having a number of components mounted on it. It protects in the event the components on the PCB may be heat sensitive. It also protects in levels applied can be adjusted. Different heat levels are necessary so that occasional cold solder joints can be simply reheated to convert into a high quality connection. But, in other instances, a greater heat level is mandated because it is necessary to melt to make the electromechanical connection necessary when installing components on the PCB. Consider a manufacturing plant which processes several PCB's per minute, each passing through a series of machines which install (or stuff) the components on the PCB. The components typically will include transistors which are commonly in the form of integrated circuit components (IC) and will also include connectors, and individual circuit components such as resistors or inductors. While some are normally less sensitive to heat, there are some capacitors which are heat sensitive. While the measurement of the capacitor can increase with dielectric materials now available, such materials are in fact very touchy to heat that is applied to them. They can be damaged by the application of excessive heat.
Alternately, while the solder tip may be maintained at the right temperature, if it is applied for too long an interval, damage may result. These are factors that have to be taken into account at the time of repairing any of the PCB's which are sent to quality control (QC) and which fail the QC tests. Consider for instance a plant that manufactures 1,000 copies of a PCB per hour. A certain percentage of those will be sent back after QC testing for repairs. At this stage of production, the handful which need repairs will be further tested and the nature of the repair can then be determined. Typically, the repairs will fall into three or four categories. For one, they will either be a cold solder joint or an open solder connection. Both require resoldering. For another, an installed component may fail, thereby suggesting that component be removed by hand and a replacement for it then installed. The replacement component has to be soldered to the PCB. Rework of this sort after QC testing is relatively straight forward, but it is dependent on and subject to the QC tests and then the repair procedure. All the foregoing requires the use of a solder tip, sometimes known as a solder gun or solder iron. Whether large or small, these have the form of a handheld wand of relatively light weight. It is kept at an elevated temperature so that there is little delay in the use of the soldering tool. Nevertheless, while it is held steadily at some temperature, it may not be the right temperature to solve each and every problem that can arise with a given PCB. In the repair step, the PCB is thus tested, the flaw is identified, and the soldering tool is then used to implement the repairs. In some instances, the repairs can be done all at a common temperature. In other instances, it may require an adjustment.
The soldering tool is adjustable to a range of temperatures. Normally, a selected temperature is required for a given situation, often dependent on the type of solder used, PCB thickness, wire gauge, maximum rating of components, required product ruggedness, and so on. These variables manifest a selected temperature for QC repair selected by a process engineer or repair line supervisor. This decision is often taken from the repair staff to assure that the repair is not too hot or cold as will be exemplified below.
The present disclosure is directed to a control system which easily mechanizes the control of the tool tip temperature. This is important so that the operator need not make an analog adjustment every time a soldering operation is made. The present disclosure is directed to a controller which includes a microprocessor (CPU) cooperative with analog to digital converter (ADC) so that measurements are taken continuously of the tip temperature. The tip temperature is maintained at a set point. One aspect of control is erroneous setting of the temperature. The operator may operate by eye, that is, the joint looks good because the metal did melt and flow. This fails when a cold solder joint is made. Another problem occurs when the joint is over heated. Heat may flow up the wire into a capacitor and damage the dielectric in the capacitor. This damage, like others, will not be observed until testing, or perhaps some time later. Generally, it is better that the solder tool tip temperature be locked at some temperature selected by specification, bypassing local control. Local, or operator control will not assure repeated consistent repair. Commonly available equipment utilizes an adjustable temperature potentiometer which is adjusted to provide any desired temperature. That, however, is tedious if required for every use of the device. Typically, the situation is somewhat simplified in that most of the solder repairs occur at a common temperature. The tip temperature should be elevated or reduced only rarely. Different repair stations can be used for the more heat sensitive components installed on the PCB. Or, higher temperatures are needed for large metal members, e.g., a plug or socket on the PCB. For that reason, a second temperature from a different solder tool is needed. Rather than reset, or adjust a rotary knob or dial and then wait for one tool to stabilize at the right temperature, there being some inertia in shifting from one to another temperature, the present disclosure contemplates a programmed control system which is adjusted to a first temperature while a second temperature is provided at a second unit. Since these two temperatures are different, each device goes on further to include a simple binary switch which is just toggled easily from one to the other position, thereby locking out operator interference with the control. The appropriate determination of the voltage level is applied to the solder tip, and calibration with respect to that voltage (hence temperature) enables the desired temperature to be achieved and locked. More than that, hand readjustment is defeated. The operator simply cannot select other temperatures while doing the repairs. One temperature is the sole temperature setting and it is locked by the system. If needed, that can be overridden. The present disclosure sets out the equipment for overriding the first setting. By overriding, supervisor control is then achieved. The supervisor selected temperature, the one essential for repairing, is executed by operation of the simple binary switch and locked into the control system.
The present disclosure sets out a binary switch which is hidden within the cabinet of the solder tip temperature control system. This cabinet encloses an internal PCB for mounting all the components necessary for its operation. The PCB supports a reed switch. The reed switch responds to an external magnetic field and thereby enables hand override without requiring more complicated transactions than that. Easily, a simple motion with a magnet will render the control operative in a different mode to accomplish a different temperature. These temperatures can be preprogrammed and started so that there is no need to undertake further activities to get to the temperatures desired. Then with the right temperatures achieved, the soldering equipment can be used to accomplish the desired repairs. The repair line supervisor is equipped with a wand or pocket carried implement, similar to a long pencil or other clip mounted device have a special strength magnet in it. The magnet is moved toward and away from a selected cabinet area to operate a reed switch. The switch is toggled to override the initial operative state and switch to another state, all for the purpose of proper device calibration and setting.